Geothermal heat exchangers are well known and include closed geothermal ground horizontal or vertical loops. In a closed loop system, a loop of piping is buried underground and filled with liquid such as water or antifreeze that continuously circulates through the system.
Horizontal geothermal ground loops typically use several hundred feet of four to six feet deep trenches. Piping is laid in the trench and backfilled. A typical horizontal ground loop will employ several hundred feet of pipe for each ton of heating and cooling. The horizontal pipes can be straight pipes but are more typically coiled type, the so-called “slinky coil” configuration with overlapped loops of piping arranged horizontally along the bottom of a wide trench. See, e.g., U.S. 2011/0011558, the contents of which are hereby incorporated by reference as if recited in full herein.
Vertical or deep bore geothermal ground loops are typically placed into the ground at much deeper depths than the trench based systems, such as between 150-300 feet. In vertical geothermal ground loops, a drilling rig is used to drill 150 to 300 foot deep holes in which hairpin-shaped loops of pipe are dropped, then grouted. A typical vertical ground loop can also require several hundred feet of pipe per ton of heating and cooling. Drilling costs are more expensive than trenching excavation costs.
Despite the foregoing, there remains a need for economic alternative geothermal heat exchangers.